1. Field of the Invention
The present invention relates to a wireless communications device which can be used in common to different communications systems.
2. Description of the Related Art
In recent years, a plurality of communications systems are used in the field of mobile communications, such as representatively mobile telephone services. For example, in Japan, the Personal Digital Cellular (PDC) system employing Time Division Multiple Access (TDMA) and the Code Division Multiple Access (CDMA) system are mainly used. In other countries, GSM (Global System for Mobile Communications) employing TDMA and UMTS (Universal Mobile Telecommunications System) employing CDMA are used. To establish compatibility between these different coexisting communications systems, various techniques have been proposed.
Conventionally, in dual-mode communications devices (or transmitters) which can be used in common to two different communications systems, when one of the communications systems is being selected, the device is generally not operated in the other communications system. Most of the dual-mode communications devices select the systems by changing paths through which a signal is transferred, using a switch or the like.
Hereinafter, an exemplary wireless communications device will be described with reference to FIG. 7, in which communication is performed, switching between an full-duplex analog mode in which transmission and reception are simultaneously performed as in the CDMA technology, and a half-duplex digital mode in which transmission and reception are alternately performed as in the TDMA technology (see, for example, WO01/80436).
FIG. 7 illustrates a block configuration of a conventional dual-mode wireless communications device. As illustrated in FIG. 7, the conventional wireless communications device comprises a transmitter 110 which generates a transmit signal, a receiver 120 which processes a received signal, an antenna assembly 130 which is connected to the transmitter 110 and the receiver 120, and a controller 140 which controls the transmitter 110 and the antenna assembly 130.
The transmitter 110 includes a high frequency amplifier 111 which modulates and amplifies input transmit data to generate a transmit signal. The high frequency amplifier 111 is controlled in accordance with a gain control signal from the controller 140. An operating state, a gain, or the like of the high frequency amplifier 111 are changed between an analog mode and a digital mode, thereby generating a transmit signal different between the analog mode and the digital mode.
The transmit signal output from the high frequency amplifier 111 is input to a common terminal A of a first path select switch 131 (single-pole double-throw switch) provided in the antenna assembly 130. The first path select switch 131 is switched in accordance with a switch control signal from the controller 140 so that continuity is established between the common terminal A and a terminal B in the analog mode, and between the common terminal A and a terminal C in the digital mode.
The terminal C of the first path select switch 131 is connected to a terminal F of a the second path select switch 132 (single-pole double-throw switch) which is switched in association with the first path select switch 131. In an operation in the digital mode, there is continuity between the terminal F of the second path select switch 132 and a common terminal D to which an antenna 134. Therefore, in the case of the digital mode, a transmit signal input to the common terminal A of the first path select switch 131 is transferred via the terminal C of the first path select switch 131 and the terminal F of the second path select switch 132 to the antenna 134 connected to the common terminal D of the second path select switch 132, and is transmitted from the antenna 134.
In an operation in the analog mode, the common terminal A of the first path select switch 131 is connected to the terminal B, and the common terminal D of the second path select switch 132 is connected to a terminal E, in accordance with a switch control signal from the controller 140. The terminal B of the first path select switch 131 is connected to a transmit signal input terminal of a duplexer 133, and the terminal E of the second path select switch 132 is connected to an antenna terminal of the duplexer 133. Therefore, in the case of the analog mode, a transmit signal input to the common terminal A of the first path select switch 131 is output via the duplexer 133 from the antenna 134.
Also in the case of the analog mode, a receive signal is received through the antenna 134 at the same time when a transmit signal is transmitted. The received signal is transferred via the common terminal D and the terminal E of the second path select switch 132 into the antenna terminal of the duplexer 133. The duplexer 133 extracts a required frequency from the received signal, separates the frequency signal from a transmit signal, and outputs the frequency signal through a received signal output terminal of the duplexer 133. The received signal output from the duplexer 133 is demodulated by an amplifier/demodulator 121 provided in the receiver 120, and the resultant signal is output as received data.
As described above, by switching the first path select switch 131 and the second path select switch 132 in accordance with a control signal from the controller 140, a signal channel including the duplexer 133 is selected in the case of the analog mode (full-duplex, i.e., a simultaneous transmission and reception operation), and a signal channel not including the duplexer 133 is selected in the case of the digital mode (half-duplex, i.e., an alternate transmission and reception operation).
Also, by controlling an operating point of the high frequency amplifier 111 in accordance with a gain control signal from the controller 140, the high frequency amplifier 111 is nonlinearly operated in the analog mode, and the high frequency amplifier 111 is linearly or quasi-linearly operated in the digital mode. Further, a gain of the high frequency amplifier 111 is adjusted in accordance with the gain control signal so as to prevent a power difference from occurring in a signal to be transmitted through the antenna 134, depending on the presence or absence of the duplexer 133.
However, the conventional exemplary wireless communications device has the following problems.
Firstly, the high frequency amplifier 111 is nonlinearly operated in the analog mode, and the high frequency amplifier 111 is linearly or quasi-linearly operated in the digital mode, so that it is difficult to maximize the power efficiency of the high frequency amplifier 111 in both the modes, i.e., the power efficiency of the high frequency amplifier 111 decreases in at least one of the modes.
Next, in the analog mode, a transmit signal from the high frequency amplifier 111 is attenuated when the transmit signal is passed through the duplexer 133. When an optimal size of the high frequency amplifier 111 is designed, taking into consideration the attenuation of a transmit signal in the duplexer 133, the power efficiency decreases in a digital mode in which there is not the attenuation of the transmit signal due to the duplexer 133.
Further, in a digital mode in which an amplitude-modulated component is included in a transmit signal, since the linearity of the high frequency amplifier 111 is important in terms of the characteristics of the modulation technique, the high frequency amplifier 111 needs to be operated in a region slightly below a saturated power point, so that the power efficiency further decreases.
In addition, not only when an analog mode and a digital mode coexist, but also when there are different digital modes, since required transmit power varies among the modes, it is considerably difficult to operate the high frequency amplifier 111 with maximum efficiency in all the modes.